/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Function;
import com.google.common.base.Objects;
import java.io.Serializable;
import javax.annotation.Nullable;

/**
 * An ordering that orders elements by applying an order to the result of a function on those
 * elements.
 */
@GwtCompatible(serializable = true)
final class ByFunctionOrdering<F, T> extends Ordering<F> implements Serializable {
    final Function<F, ? extends T> function;
    final Ordering<T> ordering;

    ByFunctionOrdering(Function<F, ? extends T> function, Ordering<T> ordering) {
        this.function = checkNotNull(function);
        this.ordering = checkNotNull(ordering);
    }

    @Override
    public int compare(F left, F right) {
        return ordering.compare(function.apply(left), function.apply(right));
    }

    @Override
    public boolean equals(@Nullable Object object) {
        if (object == this) {
            return true;
        }
        if (object instanceof ByFunctionOrdering) {
            ByFunctionOrdering<?, ?> that = (ByFunctionOrdering<?, ?>) object;
            return this.function.equals(that.function) && this.ordering.equals(that.ordering);
        }
        return false;
    }

    @Override
    public int hashCode() {
        return Objects.hashCode(function, ordering);
    }

    @Override
    public String toString() {
        return ordering + ".onResultOf(" + function + ")";
    }

    private static final long serialVersionUID = 0;
}
